creating environments in package's C code

Dear developers,

is it possible to create environments in C code of packages?
Simply using
 SEXP env;
 PROTECT (env  = allocSExp(ENVSXP));
and assigning the enclosing environment with SET_ENCLOS seems to be 
insufficient.

Best wishes,

Here's a function I use in rapache to create one:

static SEXP NewEnv(SEXP enclos){
     SEXP env;
     PROTECT(env = allocSExp(ENVSXP));

     SET_FRAME(env, R_NilValue);
     SET_ENCLOS(env, (enclos)? enclos: R_GlobalEnv);
     SET_HASHTAB(env, R_NilValue);
     SET_ATTRIB(env, R_NilValue);

     UNPROTECT(1);

     return env;
}


and an example that creates a new environment and then assigns a 
variable named OK an integer vector length 1 with value 0:

SEXP env = NewEnv(R_GlobalEnv);
defineVar(install("OK"),NewInteger(0),env);

Best

Jeff